140 lines
4.6 KiB
C
140 lines
4.6 KiB
C
/*
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* linux/include/linux/timecounter.h
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*
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* based on code that migrated away from
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* linux/include/linux/clocksource.h
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*/
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#ifndef _LINUX_TIMECOUNTER_H
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#define _LINUX_TIMECOUNTER_H
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#include <linux/types.h>
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/* simplify initialization of mask field */
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#define CYCLECOUNTER_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
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/**
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* struct cyclecounter - hardware abstraction for a free running counter
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* Provides completely state-free accessors to the underlying hardware.
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* Depending on which hardware it reads, the cycle counter may wrap
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* around quickly. Locking rules (if necessary) have to be defined
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* by the implementor and user of specific instances of this API.
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*
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* @read: returns the current cycle value
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* @mask: bitmask for two's complement
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* subtraction of non 64 bit counters,
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* see CYCLECOUNTER_MASK() helper macro
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* @mult: cycle to nanosecond multiplier
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* @shift: cycle to nanosecond divisor (power of two)
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*/
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struct cyclecounter {
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cycle_t (*read)(const struct cyclecounter *cc);
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cycle_t mask;
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u32 mult;
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u32 shift;
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};
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/**
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* struct timecounter - layer above a %struct cyclecounter which counts nanoseconds
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* Contains the state needed by timecounter_read() to detect
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* cycle counter wrap around. Initialize with
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* timecounter_init(). Also used to convert cycle counts into the
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* corresponding nanosecond counts with timecounter_cyc2time(). Users
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* of this code are responsible for initializing the underlying
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* cycle counter hardware, locking issues and reading the time
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* more often than the cycle counter wraps around. The nanosecond
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* counter will only wrap around after ~585 years.
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*
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* @cc: the cycle counter used by this instance
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* @cycle_last: most recent cycle counter value seen by
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* timecounter_read()
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* @nsec: continuously increasing count
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* @mask: bit mask for maintaining the 'frac' field
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* @frac: accumulated fractional nanoseconds
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*/
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struct timecounter {
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const struct cyclecounter *cc;
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cycle_t cycle_last;
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u64 nsec;
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u64 mask;
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u64 frac;
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};
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/**
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* cyclecounter_cyc2ns - converts cycle counter cycles to nanoseconds
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* @cc: Pointer to cycle counter.
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* @cycles: Cycles
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* @mask: bit mask for maintaining the 'frac' field
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* @frac: pointer to storage for the fractional nanoseconds.
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*/
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static inline u64 cyclecounter_cyc2ns(const struct cyclecounter *cc,
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cycle_t cycles, u64 mask, u64 *frac)
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{
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u64 ns = (u64) cycles;
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ns = (ns * cc->mult) + *frac;
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*frac = ns & mask;
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return ns >> cc->shift;
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}
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/**
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* timecounter_adjtime - Shifts the time of the clock.
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* @delta: Desired change in nanoseconds.
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*/
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static inline void timecounter_adjtime(struct timecounter *tc, s64 delta)
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{
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tc->nsec += delta;
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}
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/**
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* timecounter_init - initialize a time counter
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* @tc: Pointer to time counter which is to be initialized/reset
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* @cc: A cycle counter, ready to be used.
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* @start_tstamp: Arbitrary initial time stamp.
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*
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* After this call the current cycle register (roughly) corresponds to
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* the initial time stamp. Every call to timecounter_read() increments
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* the time stamp counter by the number of elapsed nanoseconds.
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*/
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extern void timecounter_init(struct timecounter *tc,
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const struct cyclecounter *cc,
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u64 start_tstamp);
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/**
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* timecounter_read - return nanoseconds elapsed since timecounter_init()
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* plus the initial time stamp
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* @tc: Pointer to time counter.
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*
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* In other words, keeps track of time since the same epoch as
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* the function which generated the initial time stamp.
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*/
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extern u64 timecounter_read(struct timecounter *tc);
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/**
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* timecounter_cyc2time - convert a cycle counter to same
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* time base as values returned by
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* timecounter_read()
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* @tc: Pointer to time counter.
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* @cycle_tstamp: a value returned by tc->cc->read()
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*
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* Cycle counts that are converted correctly as long as they
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* fall into the interval [-1/2 max cycle count, +1/2 max cycle count],
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* with "max cycle count" == cs->mask+1.
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*
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* This allows conversion of cycle counter values which were generated
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* in the past.
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*/
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extern u64 timecounter_cyc2time(struct timecounter *tc,
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cycle_t cycle_tstamp);
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#endif
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